The present invention generally relates to a rotary mower having a pair of cutter blades which are arranged in a cutter housing for horizontal rotation and more particularly, to a mulching mower in which grass clippings, mown and then cut finely by cutter blades, are discharged to the cut grass path and are submerged as mulch under the grass surface at the cut grass path.
Hitherto, a mower, which has a pair of horizontally rotating cutter blades arranged to the right and to the left in a downwardly opening cutter housing has been known, for example, as shown in Japanese Patent Publication No. Hei 6-75445 (1994) (hereinafter "JP '445").
In the mower disclosed in JP '445, right and left cutter blades are arranged so as to be staggered in front and rear directions so that the loci of rotation of the right cutter blade overlaps the loci of rotation of the left cutter blade in the vicinity of the longitudinal center line of the mower, when viewed from the front. Further, the cutter blade on the right side, with respect to the running direction, rotates clockwise and the cutter blade on the left side, with respect to the running direction, rotates counterclockwise. In this way, grasses, which have been trampled down ahead of the mower by the front wheels thereof, can be mowed surely by the right and left cutter blades.
The mower of JP '445 is of a rear discharge type having a discharge port provided in a rear wall section of the cutter housing and discharge scroll guide plates for guiding grasses, mown by the right and left cutter blades, to the discharge port. The mown grasses are received in a grass bag or discharged directly on the cut grass path to the rear of the mower. When the mown grasses are received in a grass bag, the cut grass clippings must be emptied from the grass bag. When the mown grasses are discharged directly on the cut grass path, discharged grass clippings fall on the cut grass path unevenly to deteriorate the appearance of the cut grass path and grasses discharged at a place where the grass clippings become piled up are apt to be blasted due to poor air ventilation.
Compare with this, in the mulching mower of the present invention, grass clippings cut by the cutter blade are discharged comparatively evenly onto the cut grass path directly below the cutter housing from the upper side so that such inconveniences as mentioned above can be avoided.
In FIG. 5 of U.S. Pat. No. 5,133,176 (hereinafter "the '176 patent"), a mulching mower is shown, which has a plurality of horizontally rotating blades arranged to the right and left in a downwardly opening cutter housing. The rotating blades are staggered to the front and to the back to overlap similarly to the rear discharge type mower of JP '445.
The mulching mower of the '176 patent has a cutter housing with a side wall which hangs down along the peripheral edge. Within the cutter housing, shrouds hang down which surround three cutter blades arranged to form circular cutting chambers. The shrouds are connected to each other through opening portions so that the circular cutting chambers communicate with each other and the shrouds form an enclosure wall completely surrounding an outer periphery of the three cutter blades in the arrangement.
The three cutter blades are arranged to rotate in the same direction within the enclosure wall. In each of the cutting chambers, kickers are provided which are projected from an under surface of an upper wall so that grass clippings, cut by the cutter blade and circulating within the cutting chamber, are deflected downwardly by the kickers to be discharged directly below and onto the cut grass path.
In the conventional mulching mower of the '176 patent, since the enclosure wall, which completely surrounds an outer periphery of a plurality of cutter blades in the arrangement, must be independently formed within the cutter housing, the cutter housing becomes large compared with the range of rotation of the cutter blades and accordingly, the weight is increased.
In addition, since all of the cutter blades rotate in the same direction, the grass clippings are apt to be biased to the right side or to the left side in the enclosure wall surrounding the cutter blades in the arrangement, and it is difficult to discharge the grass clippings so as to be dispersed uniformly over the entire area under the cutter housing. In order to ensure uniform dispersion of the grass clippings, it is necessary to provide kickers for each of the cutter blades for dropping grass clippings, cut by a cutter blade, beneath the same cutter blade. Therefore, the construction of the mulching mower becomes complicated.
Generally, the mulching mower has no discharge port at the side wall section. Therefore, mown grass clippings are circulated along the inner surface of the enclosure wall, which surrounds the outer periphery of the cutter blade. The mown grass clippings are dispersed evenly and discharged downwardly, out of the cutter housing by downwardly directed wind at the outer periphery of the cutter blade caused by rotation of the cutter blade.
However, at a juncture portion where tip end rotation loci of adjacent cutter blades approach each other, and where the enclosure wall cannot be provided, a communicating opening is formed as described above, and the grass clippings are not guided by any enclosure wall. Therefore, an especially large quantity of grass clippings fall down at the juncture portion. As the result, the grass clippings do not fall on the cut grass path so as to be dispersed evenly and unsightly clumps of mown grass clippings are left on the lawn.
Further, at the juncture portion, the wind blows out downwardly to cause uncut grasses to lay down before the cutter blade passes over them, so that the uncut grasses are apt to be left behind.
Since grasses to be cut by the cutter blade contain a large amount of water, the cut grass clippings will adhere to the inner surface of the enclosure wall. The grass clippings which adhere to the enclosure wall are scraped off by outer ends of the rotating cutter blade, but if the scraping off of the grass clippings from the enclosure wall is not carried out sufficiently, large clumps of the grass clippings fall down periodically or the grass clippings which adhere to the enclosure wall lock the cutter blade so that sometimes continuation of the mowing function by the mower becomes impossible.
By the way, Japanese Laid-Open Utility Model Publication No. Hei 4-55226 (1952) (hereinafter "JP '226") discloses a mower having upper and lower cutter blades, rotating approximately horizontally, provided on a lower end portion of an approximately vertical rotary shaft, in which a cutting edge of the upper cutter blade is positioned ahead of the cutting edge of the lower cutter blade in the direction of the blade rotation so that tip end parts of the grasses are cut by the upper cutter blade first and then, lower parts of the grasses are cut by the following lower cutter blade, and the grasses are thereby finely cut.
In the mower of JP '226, the width, in the rotational direction of the cutting edge portion of the lower cutter blade, is made wider than the width of the upper cutter blade to form a ventilating passage between the upper and lower cutting edge portions. The cutting edge portion of the lower cutter blade is provided with a rising portion, at the rear side with respect to the direction of rotation, for changing the direction of the wind within the ventilating passage upwardly.
Generally, a rising portion (feather portion) such as is formed on a rear side of a cutting edge portion of a cutter blade, is provided for generating a pulsatile wind within the cutter housing by rotation of the cutter blade. Grasses are raised by pulsation of the wind and cut by the cutter blade. Therefore, the grasses can be mown simply with a good finish.
Further, in the mulching mower of JP '226, finely cut grass clippings are dispersedly discharged onto the lower cut grass path from the cutter housing by the pulsation of the wind and pushed under the grass surface of the cut grass path. Therefore, it is unnecessary to dump the cut grass clippings in a suitable place in order to maintain the pleasing aesthetic look of the cut grass path.
In order to generate wind pulsation sufficient to dispersedly discharge the grass clippings within the cutter housing, the rising portion must be of a considerable height. Particularly, in the mower of JP '226, while grasses are cut by tow upper and lower cutter blades, the wind pulsation is generated by the rising portion formed on the lower cutter blade only, so that it is difficult to obtain the amount of wind necessary for raising the grasses.
If the rising portion is made of a considerable height, the necessary amount of wind can be obtained. But in this case, because air resistance and resistance by grass clippings acting on the rising portion are increased, the strength of the cutter blade must be increased. Thus, the lower cutter blade becomes robust and heavy and the cost thereof is also increased.
In addition, since the upper and lower blades are very different in shape and construction, different upper and lower blades must be provided in the manufacture of the mower and also, two kinds of cutter blades must be prepared for use of the mower. This is disadvantageous in respect of both production and maintenance.